Ecologists, economists, and psychologists have called attention to some provocative similarities among the optimal forager, the optimal consumer in the economic marketplace, and the laboratory animal performing under the constraints of a contingency schedule. Toward further examination of these similarities the proposal elaborates two integrative concepts, behaviora substitutes and complements. The proposal describes a way of measuring the intrinsic substitutability or complementarity of any pair of behaviors, and a way of measuring independently their role in the animal's response to the constraints of a schedule. The project deals with two pairs of behaviors in the rat: licking an empty tube vs. a water tube and saccharin vs. water. Intrinsic relations are measured under a baseline condition that allows free performance of one response but varies experimentally the total amount of the other response. The slope of the baseline curve measures intrinsic substitutability (negative slope), complementarity (positive slope), or independence (zero slope). Subsequently we measure a similar schedule curve by testing the rat under several fixed-ratio schedules that require instrumental performance of one response for contingent access to the other response. By comparing the baseline curve with the schedule curve we can determine which aspects of performance under the schedule reflect intrinsic relations between the two behaviors, and which do not.